Teaching Workshop: Color Vision in Primates and Other Mammals

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1 Teaching Workshop: Color Vision in Primates and Other Mammals Carrie C. Veilleux & Amber Heard-Booth Anthropology Department, University of Texas at Austin

2 Trichromatic Color Vision

3 Trichromatic Color Vision

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5 Dichromatic Color Vision

6 Trichromat Dichromat

7 How does this work? Dichromats have 2 types of color-detecting cells in the retinas in their eyes: Blue-sensitive cones Yellow/green-sensitive cones

8 Dichromat Green cone Blue cone -

9 How does this work? Trichromats have 3 types of colordetecting cells in the retinas in their eyes: Blue-sensitive cones Yellow/green-sensitive cones Red-sensitive cones

10 Dichromat Trichromat Green cone Blue cone - Red cone Green cone Blue cone - -

11 Most mammals are dichromats

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14 Many primates are trichromats

15 Dichromats see a square Trichromats see a square and a circle

16 Dichromatic animals and people can actually detect camouflaged objects better than trichromats

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18 Physiology of Color Vision Cone photoreceptors

19 Physiology of Color Vision Photopigment Opsin protein chromophore opsin protein chromophore (11-cis retinal)

20 Physiology of Color Vision (Fasick et al. 2002) Cone spectral sensitivity (color of light to which it responds) is determined by structure of opsin protein (amino acid sequence of protein). Amino acid sequence is determined by opsin genes.

21 Physiology of Color Vision So, changes in the DNA sequence of an opsin gene can lead to differences in the spectral sensitivity of cones ( critical tuning sites ). critical tuning sites of the M/L opsin gene Nathans (1999)

22 Physiology of Color Vision So, changes in the DNA sequence of an opsin gene can lead to differences in the spectral sensitivity of cones ( critical tuning sites ). green sensitive (543 nm) M/L Opsin Gene site 285 T G G G G A C C C T A C G C C Alanine (Ala) T G G G G A C C C T A C A C C Threonine (Thr) red sensitive (558 nm)

23 Physiology of Color Vision So, changes in the DNA sequence of an opsin gene can lead to differences in the spectral sensitivity of cones ( critical tuning sites ). Alanine Threonine M/L Opsin Gene site 285 λ max ~ 543 nm λ max ~ 558 nm

24 Physiology of Color Vision The number of cone types with different spectral sensitivities determines the type of color vision an animal has. Color vision = ability to discriminate light of different spectral qualities independent of intensity For color vision, need: 1) 2+ cone types 2) Neural mechanisms to compare cone outputs

25 Physiology of Color Vision Color vision and primate opsin genes: Dichromacy (ancestral mammal condition) Chromosome 7 S Opsin Gene X Chromosome M/L Opsin Gene

26 Physiology of Color Vision Color vision and primate opsin genes: Polymorphic trichromacy (NWM & lemurs) Chromosome 7 S Opsin Gene X Chromosome M/L Opsin Gene M/L Opsin Gene Multiple alleles with different spectral sensitivities (2-5 alleles!)

27 Physiology of Color Vision Color vision and primate opsin genes: Polymorphic trichromacy (NWM & lemurs) Male Homozygous Female Heterozygous Female Ch. 7 S Opsin Ch. 7 S Opsin Ch. 7 S Opsin Ch. X any allele Ch. X Ch. X 543nm allele 543nm allele Ch. X Ch. X 543nm allele 563nm allele DICHROMAT DICHROMAT TRICHROMAT

28 Physiology of Color Vision Color vision and primate opsin genes: Routine trichromacy (catarrhines & Alouatta) Chromosome 7 S Opsin Gene X Chromosome L Opsin Gene M Opsin Gene Duplication of M/L opsin gene leading to divergent L and M opsin genes. Routine trichromacy evolved independently in catarrhines and howlers.

29 Primates are unique among placental mammals in having trichromatic color vision BUT primate color vision is not impressive compared to other vertebrates!

30 Why be a trichromat?

31 Search Activity: Why be a trichromat? Based on an experiment done in marmoset monkeys Some individuals were dichromats, some individuals were trichromats Monkeys foraged for orange or green Kix cereal in green wood shavings

32 Search Activity for Humans Activity Goals: 1. Explore differences in color recognition among different people 2. Identify possible benefits of having trichromatic color vision for primates 3. Explore the effects of red-green colorblindness in humans